Calcium regulation in cardiac myocytes is central to excitation-contraction coupling (ECC) and in mitochondrial and hypertrophic (Hyp) nuclear signaling. Ubiquitous Ca regulatory systems, Ca-calmodulin (CaM) dependent protein kinase II (CaMKll), calcineurin and inositol (1,4,5)P3 receptors (InsP3R) in myocytes have been implicated in altering ECC, arrhythmogenesis and nuclear signaling. This PPG has advanced understanding of these emergent fields during the current award. In this renewal, novel questions & methods will be used to deepen understanding of these areas with respect to ECC, mitochondrial signaling, Hyp & heart failure (HF). Four highly synergistic multidisciplinary projects are planned. Project I (Bers) focuses on critical aspects of cellular CaMKll in aims concerning: 1) acute CaM & CaMKll effects on ECC, 2) Ca/CaM-dependent nuclear signaling via HDAC and NFAT, 3) quantitative aspects of mitochondrial Ca signaling, and 4) altered CaMKll signaling in Hyp & HF (regarding ECC, arrhythmias & nuclear regulation). Project II (Blatter) focuses on cellular aspects of IP3 signaling in 3 aims (Hyp & HF) concerning: 1) acute IP3R-mediated effects on ECC and arrhythmias, 2) the role of InsP3R in mitochondrial Ca signaling and oxidative stress, and 3) Ca coding and IP3R involvement in nuclear NFAT signaling. Project III (Molkentin) focuses on Ca signaling and hypertrophic signaling and will assess how 1) altered Na influx via Na channels and 2) altered Na efflux via Na/K-ATPase regulate myocyte Ca and Hyp, and 3) how cyclophilin D & permeability transition pore regulate mitochondrial Ca. Project IV (Brown) focuses on CaMKll isoform-specific targets and localization by assessing 1) CaMKIldeltaB(B vs. CaMKIldeltaC(c localization and targets, 2) functional consequences of CaMKll compartmentalization, 3) how CaMKll is involved in post-ischemic signaling and 4) how CaMKll alters mitochondrial function. Scientific cores will support these aims. Core B (Genefic Mouse Models) will develop unique mice (e.g. KO/transgenics for InsP3R, CaMKIIdelta/gamma(, PKD, Epac1/2) for whole animal & myocyte studies. Core C (HF Rabbits) will prepare and do some analysis of HF rabbits. This integrates experienced investigators with highly complementary expertise and perspective to tackle these questions in an interactive multidisciplinary approach. Results will greatly increase our understanding of the roles of CaMKll and InsP3R in cardiac myocytes during ECC, arrhythmogenesis & nuclear signaling in normal, Hyp and HF cardiac myocytes.